An important use of Coordinate Measuring Machines (CMM) is the inspection of manufactured workpieces to insure that they meet manufacturing specifications. Commonly, the CMM includes a computer program to take a series of readings of coordinate data at various locations on the workpiece, in order to perform a complete inspection of the desired dimensions of the workpiece. A determination can then be made as to whether the workpiece is of acceptable quality, or whether it should be rejected. Currently, inspection of workpieces using CMMs involves placing a workpiece on an inspection table and activating a computer program that prompts the CMM probe to the proximity of the workpiece, prompts a position alignment qualification step of the probe with respect to the workpiece, then prompts the probe to perform the inspection. This time consuming position alignment qualification step needs to repeat with every workpiece as, without it, the CMM probe may crash into the workpiece and incur damage as it is seeking its surface. Furthermore, conveying heavy workpieces to the CMM measurement area may be time consuming as well as risks personal injury and damage to the measurement area if not performed with a great deal of care.
Prior art references disclose a number of ways to correct for calibration errors and improve calibration speed.
U.S. Pat. No. 4,561,050 relates in general to machining centers having a plurality of tools for successively machining a workpiece. More specifically, the invention provides an arrangement for automatically taking into account different lengths of successively used tools so as to relieve the operator of extensive “adjustment” each time one tool is exchanged for another.
U.S. Pat. No. 4,796,195 discloses a method for effecting numerically controlled machining operations at a predetermined location. A reference feature is fixed proximate to the predetermined location and the location of a reference surface is measured prior to machining to produce surface signals representing the coordinates of the reference surface. Location correction signals are produced in response to the reference surface signals.
U.S. Pat. No. 5,471,406 refers to a method for the rapid measurement of workpieces having elemental shapes of known geometry in any orientation in space. The elemental shapes are scanned on a CMM equipped with a measuring probe head having a permissible measurement range (MR).
The method in U.S. Pat. No. 5,610,846 is used to determine the elastic bending of CMMs as a result of the measuring force and the position of measuring slides in the measuring range of the machine. Correction values are determined, which are used to compensate for measuring errors caused by machine bending. The correction values are a function of the position of the measuring slides and on the measuring force between the probe of the coordinate measuring machine and workpieces within the measuring range and are established and stored for several positions.
U.S. Pat. No. 5,856,924 describes a fixture processor for automatically designing a fixture design based on input criteria and constraints. The electronic processor uses mathematical calculations and iterations that are used in design optimization algorithms. The output of the fixture processor designates the locations for optimal securing of the workpiece for inspection for which vices and jaws are used.
Japanese Patent number JP 7324928 teaches a method for storing the coordinates of a measuring machine's deformation characteristics as a function of the measuring slider position and slider acceleration in the form of correction values and subsequently, data measured by the CMM are corrected when a workpiece is subjected to its coordinates' measurement by means of correction values.
None of the prior art references identified relate to workpiece measurement replication and no references that address the issue of conveying and positioning various workpieces for coordinate measurements have been identified.